If you asked people to name one full Moon, the top vote getter would be the one that lights up the sky tonight: the Harvest Moon — the full Moon that’s closest to the start of autumn in the northern hemisphere.

For most of the modern world, the Harvest Moon is little more than romantic folklore. But before automation and electric lights, it was a big help to farmers because it allowed them to work their fields well into the night.

And that’s not just because of the Moon’s brightness. It’s also because the Moon rises close to the same time for a few nights after the Harvest Moon — right around sunset.

The effect is more pronounced as you go farther north. From states like Minnesota and Washington, the Moon rises only about 30 minutes later tomorrow night than it does tonight, compared to an average of about 50 minutes later over a full year. At those latitudes, where the frosts come early, every hour of harvesting could make a big difference.

Perhaps because of its big reputation, many people think the Harvest Moon must look bigger than other full Moons, but it doesn’t. The Moon’s apparent size depends on its distance, which can vary by about 10 percent. But the distance isn’t related to the Moon’s phases. For this Harvest Moon — which officially is around dawn tomorrow — the Moon is slightly closer than average, but not by much.

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